Multicolor screen-carrying element in additive color photographic processes



E. H. LAND 3,536,488 MULTICOLOR SCREEN-CARRYING ELEMENT IN ADDITIVE Oct.27, 1970 COLOR PHOTOGRAPHI C PROCESSES 2 Sheets-Sheet 1 Filed June 13,1968 INVENTOR. 6M 151M BY b/ww n WM amal ATTORNEYS Oct. 27, 1970 E H.LAND 3,536,488

MULTICOLOR SCREEN-(iARRYING ELEMENT IN ADDITIVE COLOR PHOTOGRAPHICPROCESSES Filed June 13, 1968 2 Sheets-Sheet 2 FIG. 4

FIGS

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INVEIJTQR. gum a. aami Elwum and 772m anwl W 7% Jo'ad ATTORNEYS UnitedStates Patent 3,536,488 MULTICOLOR SCREEN-CARRYING ELEMENT IN ADDITIVECOLOR PHOTOGRAPHIC PROCESSES Edwin H. Land, Cambridge, Mass, assignor toPolaroid Corporation, Cambridge, Mass., a corporation of Delaware FiledJune 13, 1968, Ser. No. 736,796 Int. Cl. G03c 7/04 US. Cl. 96-24 44Claims ABSTRACT OF THE DISCLOSURE Photographic element for additivecolor photographic process comprising, on one of its surfaces, amulticolor screen with a photosensitive silver halide emulsioncontaining at least two halides selected from iodides, bromides andchlorides, and containing also silver precipitating nuclei.

The present invention relates to photography and, more particularly, tophotographic products and processes specifically adapted for colorreproduction in accordance with the principles of additive colorphotography.

In general, color photographic reproduction may be provided by exposinga photoresponsive material such as, for example, a photosensitive silverhalide emulsion, to selected subject matter through an optical screenelement possessing filter media or screen elements of selected radiationmodulating characteristics such as filter media selectively transmittingpredetermined portions of the electromagnetic radiation spectrumsvisible segment. The color information thus recorded is read out byviewing resultant image conformation in the photoresponsive materialthrough the same or a similar screen element in appropriate registrationwith the image. For the reproduction of subject matter in color and inaccordance with the principles of additive color photography, theindividual filter media or screen elements constituting the opticalscreen will be constructed to effect selective filtration ofpredetermined portions of the visible electromagnetic spectrumsubstantially corresponding to its red, blue and green regions and colorinformation recordation is accomplished by point-to-point incidence ofradiation actinic to the selected photoresponsive material as modulatedby such screen element. Visual reproduction of the information contentrecorded by the photoresponsive material is accomplished by read out ofthe impressed image as modulated by the original or a substantiallyidentical screen element in accurate registration with the image record.

Additive color photographic reproduction thus may be provided byexposing a photoresponsive material, preferably a photosensitive silverhalide emulsion, through an additive color screen having a plurality offilter media or screen element sets each of an individual additive colorsuch as, red, blue or green, and by viewing the resultant photographicimage, preferably a silver image, subsequent to development of suchimage, through the same or a substantially identical screen elementsuitably registered.

Although for color information recordation purposes, the photoresponsivematerial and optical screen may comprise separate and distinct elementsappropriately registered during periods of exposure and viewing and theoptical screen element may be temporarily or permanently positioned onthe surface of a transparent carrier opposite that retaining thephotoresponsive material, for practical purposes, it is preferred topermanently position the photoresponsive material in direct contiguousrelationship to the color screen during exposure, in order to maximizethe acuity of the resultant image record.

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Subsequent to exposure of the photoresponsive material to actinicradiation transmitted through and filtered by the optical screen, theresultant photoexposed element may be further processed, where required,in accordance with the materials selected and generally without regardto the filter screen when the latter element is stable with respect toand/or protected from contact with the processing compositions andcomponents selected. Such protection and stability will ordinarily beenhanced and facilitated by disposition of the filter screen between atransparent, processing composition impermeable carrier and thephotoresponsive material, and, in particular, where such configurationadditionally includes the presence of a processing composition barrierelement or layer intermediate the screen and the photoresponsivematerial.

Subsequent to selective exposure of, for example, the preferredphotoresponsive material, that is, photosensitive silver halide, theresultant exposed material may be processed in the same manner asblack-and-White photographic film is conventionally processed. Thephotoexposed emulsion thus may be developed by any of the conventionaldeveloping procedures known in the art to be adapted to effect reductionof photoexposed silver halide crystals. In general, such developmentwill be effected by contact of the photoexposed emulsion with a solutioncontaining a conventional developing agent such as one or more of theconventional developing agents and compositions of same set forth inchapter 14 of The Theory of the Photographic Process (revised edition1954), C. E. K. Mees, The Macmillan Co., New York, N.Y., and chaptersVI, VII, VIII and IX of Photographic Chemistry, vol. I, P. Glafkides,Foundation Press, London, England. The preferred developing agentsgenerally comprise organic compounds and, in particular, compriseorganic compounds of the aromatic series containing at least twohydroxyl and/ or amino groups wherein at least one of such groups is inone of ortho or para positions with respect to at least one other ofsuch groups such as, for example, the various known hydroquinones,p-arninophenols, p-phenylene diamines, and their various knownfunctional homologues and analogues. The developing compositioncontaining the specific silver halide developing agents selected willgenerally comprise an aqueous solution additionally containing at leastan alkaline material such as sodium hydroxide or sodium carbonate or thelike and may be contacted with the photoexposed silver halide materialaccording to any of the conventional tray, tank, or the like,procedures. The composition may additionally and optionally contain oneor more specific silver halide developing agents, preservatives,alkalis, restrainers, accelerators, etc., other than those specificallydenoted in the cited reference material. The concentration of thevarious components employed may be varied over a wide range and, wheredesirable, any one or more of such components may be disposed in thephotosensitive element, prior to exposure, and in a separate permeablelayer of such element and/or in the emulsion comprising thephotosensitive silver halide material itself.

For the purpose of stabilizing the developed image, the emulsion may befixed in any of the conventional fixing, washing, and/ or dryingprocedures known in the art as, for example, those described in chapterXI of Photographic Chemistry, vol. I, supra, and chapter 17 of TheTheory of the Photographic Process, supra. For example, thephotosensitive material retaining the developed image may be initiallycontacted with a stop bath adapted to terminate action of the developingagent on the photosensitive emulsion by converting the pH of theemulsion to that at which the selected silver halide developing agent oragents exhibit substantially no developing potential. Specifically,where the silver halide developing agent is organic compound exhibitingits developing action in an alkaline pH, for example, a hydroquinone, orthe like, the emulsion may be subjected to an acid stop bath for asufiicient time interval as to eflectively neutralize the silver halidedeveloping potential of the selected developing agent.

The emulsion may then be subjected to a fixing bath in order to effectremoval of unexposed photoresponsive silver halide from the emulsion inaccordance with the conventional procedures known to the art as adaptedto effect same and as further detailed in the last cited references.

In general, the fixing agent employed may comprise a bath of a silverhalide solvent such as sodium thiosulfate which is effective to removesubstantially all types of silver halides from disposition in theemulsion strata originally containing the photosensitive silver halidewithout deleterious attack upon the conformation of the developed silverimage. Subsequent to fixation, all residual traces of the fixing agentmay be removed by aqueous wash contact, in order to insure thepermanency of the developed image.

Where positive silver image formation is desired, that is, an imageprovided in terms of unexposed portions of the emulsion, reversalprocessing may be employed in its conventional manner, or a directpositive emulsion may be employed, or the positive image may be providedby diffusion transfer processing.

In the first alternative denoted above, the reversal processing may beaccomplished in the conventional manner by developing the photoexposedemulsion by any of the conventional procedures known in the art asadapted to effect development of the latent image resultant fromphotoexposure such as, for example, the procedures identified above.Subsequent to development of the latent image to a visible silver image,the resultant developed image may be effectively removed in theconventional manner by contact of the image with any of the conventionalagents known in the art as adapted to effect removal of a photographicsilver image without deleterious effect upon unexposed photosensitivesilver halide such as, for example, the bleaching agents and bleachingbaths set forth in chapter XXX of Photographic Chemistry, vol. II,supra. Subsequent to the removal of the developed image by, for example,bleaching, the photosensitive silver halide remaining in the emulsionstructure may be converted to a developable state by physical foggingresultant from, for example, exposure of actinic radiation, and/orchemical fogging, for example, by contact with a conventional foggingagent or the like, and, in turn, the resultant fogged silver halide maybe developed and, where desired, stabilized, in the manner set forthabove, to provide the requisite positive silver image formation.

In the second alternative denoted above, the equisite positive silverimage formation may be provided by employment of a conventional directpositive silver halide emulsion which may be directly developed, in thepresence of a fogging agent, according to the procedure described above,to provide the requisite positive silver image formation.

In the third alternative denoted above, the positive silver imageformation may be provided by diffusion transfer processing wherein thelatent image provided to the photosensitive silver halide emulsion byexposure is developed and, substantially contemporaneous with suchdevelopment, a soluble complex is obtained, for example, by reaction ofa silver halide solvent with unexposed and undeveloped silver halide ofthe emulsion. The resultant soluble silver complex may be, at least inpart, transported in the direction of a suitable print-receivingelement, and the silver of the complex precipitated in such element toprovide the requisite positive silver image formation. Commensurate withthe preceding alternatives denoted, the resultant positive silver image,in this embodiment, a silver transfer image, may be viewed through thesame, or a similar, color screen element which is suitably registeredWith the positive silver transfer image carried by the print-receivinglayer.

In each alternative, the preferred film units comprise apanchromatically sensitized photographic emulsion positioned contiguousa surface of a multicolor additive color screen which, in the lastalternative denoted, may possess the print-receiving elementintermediate a photographic emulsion and the color screen, either withor without a stripping layer positioned intermediate the print-receivinglayer and the emulsion layer, to facilitate separation of the emulsionlayer subsequent to transfer image formation. Employment of thepreferred integral film unit allows exposure of the emulsion to beaccomplished through a. color screen, including through a transparentsupporting member, if present, and formation of the requisite positivesilver image in contiguous relationship to the color screen employedduring exposure. Such embodiment accordingly obviates the necessity ofregistering the color screen with the resultant positive silver image,for viewing purposes, in that the screen employed for exposing may alsobe employed for viewing and is in automatic registration with thepositive silver image.

Of the three alternatives denoted above, production of the positiveimage by diffusion transfer processing is clearly preferable to thatdenoted by the first alternative in view of the effective simplicity ofthe processing involved and is clearly preferable to that of the secondembodiment by reason of the higher photographic speeds practicablyobtainable.

Although, as disclosed in US. Pat. No. 2,614,926, the positive silvertransfer image formation may be provided by an additive multicolordiffusion transfer reversal process which includes exposure of a silverhalide emulsion layer through an additive color screen and separation ofthe emulsion layer, from contact with the remainder of the film unit,subsequent to processing, while retaining filter media and receptionlayer in fixed relationship, a preferred process will comprise thatdisclosed in US Pats. Nos. 2,726,154 and 2,944,894, which are directedto a diffusion transfer reversal process which specifically includesexposure of an integral multilayer film assemblage through a screenpossessing a plurality of minute optical elements and carryingphotosensitive and image-receiving layers. As disclosed in the citedpatents, transfer processing of the exposed film may be accomplished bypermeation of the exposed integral film unit with a liquid processingcomposition and the image-receiving layer retained in permanent fixedrelationship to the screen during, and subsequent to, formation of therequisite transfer image, with the operators option of separating thephotosensitive layer from the remainder of the film unit subsequent totransfer image formation.

As disclosed in US. Pat. No. 2,712,995, direct production of a positivesilver image may also be provided by employment of a spontaneouslydevelopable silver salt dispersion, that is, a silver salt dispersionsuch as silver oxalate, silver stearate, silver ferrocyanide, or certainsilver chloride dispersions, which is directly reduced to elementalsilver in the absence of exposure to bromide ions and to actinicradiation, and thus not as a function of the pointto-point incidence ofactinic radiation. In the disclosed structure, the image-providing,spontaneously developable silver salt dispersion contains the minimalconcentration of photosensitive silver bromide required to effectrelease of bromide ions, from the silver bromide crystals upondevelopment in the absence of bromide and as a function of exposure, inthe concentration required to inhibit, imagewise, spontaneousdevelopment of the silver salt dispersion. As further stated in thecited patent, the spontaneous development reaction of the silver saltdispersion may be enhanced by the addition of substances which act asnuclei for the reaction and the employment of a processing cornpositioncontaining a silver halide solvent such as sodium sulfite. However, asdisclosed in the patentees subsequent US. Pat. No. 2,937,945, the silverimages obtained by the process of the preceding patent show the drawbackthat the whites are impaired by the negative image formed from thephotosensitive material, that is, the silver bromide dispersion. It isthere stated that it is necessary to be especially careful to keep theamount of the silver bromide as small as possible so that the visiblesilver image originating from development of such material does notexceed the critical threshold required for effective employment of theresultant image. The last-identified patent denotes the improvementwhich consists of improving the quality of resultant image bydisposition of the respective spontaneously developable silver saltdispersion and photosensitive silver bromide dispersion in separatelayers, maintained in contact during development, but separated from oneanother subsequent to formation of the positive silver image.

As disclosed in French Pat. No. 53,513, Third Addition to French Pat.No. 873,507, it was also known pre-existing the last two mentionedpatents that a primary negative image and a secondary positive image maybe provided by exposing a silver halogenide emulsion containing silverprecipitating agents and sequentially treating the thus exposed emulsionfirst with a silver halide developing formulation which does not containa silver halide solvent and then with a developer formulation which doescontain a silver halide solvent and specifically a chromogenic developerformulation containing a silver halide solvent to provide, upon thesubsequent elimination of the metallic silver images, the production ofa colored positive image.

However, for a plurality of reasons set forth in detail hereinafter, itwould be particularly desirable to possess the wherewithal to fabricatean integral film assemblage essentially comprising an optical screenelement possessing, fixedly positioned in contiguous relationship to onesurface, a photoresponsive material directly providing positive imageformation and possessing the sensitivity to incident electromagneticradiation and acuity of image formation necessary to effectively providecolor photographic image reproduction in accordance with the principlesof additive color photography.

Accordingly, it is a principal object of the present in vention toprovide new and improved photographic products, compositions andprocesses particularly adapted for the photographic reproduction ofsubject matter in color and particularly in accordance with theprinciples of additive color photography.

Other objects of the invention will in part be obvious and will in partappear hereinafter.

The invention accordingly comprises the process of the several steps andthe relation and order of one or more of such steps with respect to eachof the others, and the product possessing the features, properties andthe relation of elements which are exemplified in the following detaileddisclosure, and the scope of the application of which will be indicatedin the claims.

For a fuller understanding of the nature and objects of the invention,reference should be had to the following detailed description taken inconnection with the accompanying drawings wherein:

FIG. 1 is a diagrammatic enlarged cross-sectional view illustrating theassociation of elements constituting one embodiment of the presentinvention, the thickness of the various materials being exaggerated;

FIG. 2 is a photomicrograph of integral positive and negative silverimage formation in a maximum density area of a silver image provided, inaccordance with the present invention, at a magnification of 1280 FIG. 3is a photomicrograph of positive diffusion transfer silver imageformation in a corresponding maximum density area of a silver transferimage, provided in accordance with the teachings of US. Pat. No.2,861,885, infra, at a magnification of 1280= alt) FIG. 4 is aphotomicrograph of integral negative and positive silver image formationin a minimum density area of a silver image, provided in accordance withthe present invention, at a magnification of 1280X;

FIG. 5 is a photomicrograph of negative silver image formation in acorresponding maximum density area of the photosensitive silver halideemulsion stratum of a silver diffusion transfer film unit fabricated andprocessed in accordance with U.S. Pat. No. 2,861,885, infra, at amagnification of 1280 and FIG. 6 is a photomicrograph of negative silverimage formation in a minimum density area of the photosensitive silverhalide emulsion stratum of a silver diffusion transfer film unit,fabricated and processed in accordance with US. Pat. No. 2,861,885,infra, at a magnification of 1280 which integrates with the maximumdensity area of the silver transfer image of FIG. 3 as an integralcomposite print to be viewed by reflection or transmission.

As previously stated, a silver diffusion transfer reversal process mayprovide a positive silver transfer image by development of the latentimage provided a photosensitive silver halide emulsion by exposure and,substantially contemporaneous with such development, a soluble silvercomplex is obtained, by reaction of a silver halide solvent withunexposed and undeveloped silver halide of the emulsion. The resultantsoluble silver complex is, at least in part, transported in thedirection of a suitable print-receiving element and the silver of thecomplex there precipitated to provide the requisite positive silverimage formation.

The silver receptive stratum employed may be so constituted as toprovide an unusually effective silver precipitating environment whichcauses the silver deposited therein, in comparison with negative silverdeveloped in the silver halide emulsion, to possess an extraordinarilyhigh covering power, that is, opacity per given mass of reduced silver;see Edwin H. Land, One Step Photography, Photographic Journal, sectionA, pp. 7-15, January 1950.

Specifically, to provide such environment, silver precipitation nucleimay be disposed within the silver receptive stratum in clusterspossessing a diameter directly proportional to the mass of image silverto be deposited in situ by reduction. Such conformation can be employedto cause image silver to precipitate, in association with the silverprecipitation nuclei clusters, with the required density and of a sizedirectly related to the physical parameters of the clusters. The imagesilver thus precipitated in situ in galaxies of chosen physicalparameters provides image conformation in which the elemental silver ofthe print-receiving element may possess a very high order of coveringpower, for example, five to fifteen or more times that of the negativeelemental image silver in the silver halide element.

As disclosed in US. Pat. No. 2,861,885, desirable composite printscomprising both negative and positive images in superposition may beprovided by simplified silver diffusion transfer reversal processesemploying a photosensitive silver halide emulsion which upon fulldevelopment of its exposed areas, as a function of exposure, provides arelatively low maximum density negative silver image with relation tothe high maximum density positive silver image provided by a silverprecipitating environment of the type detailed above. In a compositeprint produced in accordance with the disclosure of the cited patent,the covering power of a given mass of image silver in theprint-receiving element is there stated to range from 14 to 15 timesthat of an equal mass of image silver in the silver halide element and,accordingly, for transparency employment a maximum negative density ofas high as 1.0 density units may be permissible where the maximumpositive density is about four or more times as great.

It has now been unexpectedly discovered that a photoresponsive material,specifically a photosensitive silver halide emulsion, fixedly maintainedin contiguous relationship to an optical screen element, may be employedto provide a direct positive visible silver image possessing the acuitynecessary for effective color reproduction in accordance with theprinciples of additive color photography. For such employment, theemulsion is specifically formulated to contain silver precipitatingnuclei dispersed throughout in a concentration effective to provide,subsequent to exposure and development with a processing compositioncontaining a silver halide developing agent and a silver halide solvent,a positive silver image derived from unexposed silver halide crystalspossessing greater covering power than the negative silver image derivedfrom exposed silver halide crystals.

In general, in accordance with the teachings of the photographic art,physically developed silver is directly reduced from a fluid phaseduring development and essentially comprises relatively compact grains.In contradistinction, chemically developed silver, in all knownconventional processes, is directly furnished from exposed silver halidecrystals and essentially includes image silver in the general form offibers or filaments. The covering power, that is, the optical densityper gram of silver per square meter, of the resultant silver image, ineach instance, is a function of the aggregation and conformation ofdeveloped silver and, in general, may be considered to be inverselyproportional to the diameter of the particles, or grains as aggregated,in the absence of considerations with respect to aggregate conformation.

In conventional development practice, employing either so-calledphysical or chemical, both types of development occur to an extent,however, chemical development is characterized by the fact that themajor portion of the developed elemental silver is derived from directchemical reduction of exposed silver halide crystals and only asubstantially inconsequential proportion of developed elemental silveris derived from solution physical development. Conversely, physicaldevelopment is characterized by the fact that a predominant proportionof the developed silver is derived from direct solution physicaldevelopment and only a minimal proportion of the resultant image silveris derived from chemical development.

In accordance with the unexpected discovery which constitutes thepresent invention, however, a photosensitive silver halide emulsion maybe fabricated to provide as a function of exposure, upon development inthe presence of a silver halide solvent, elemental silver imageformation of a character previously unknown to the photographic art.Specifically, it has been now discovered that image silver derived fromdirect development, in the presence of a silver halide solvent, ofphotoexposed silver halide crystals comprising an emulsion formulationfabricated as detailed herein, that is, photoexposed silver halidecrystals having directly associtaed therewith an effective concentrationof silver precipitating nuclei, is characterized by the substantialabsence of fiber or filamentary conformation. The image silverconformation so provide is substantially restricted to elemental silvergrains or particles possessing a diameter substantially equal to theoriginal diameter of the unexposed photosensitive crystals constitutingthe emulsion. Amplification of the thus produced negative silver imageto provide an optical density beyond that provided by elemental silverimage particles or grains of a diameter directly comparable to theemulsions original crystal diameters, generally ranging in size fromabout 1 to 3.5 microns in high speed photographic materials, resultantfrom increased image grain diameter pursuant to crystal surface areagrowth, directly or by reason of elemental silver fiber or filamentproduction, has been discovered to be effectively prevented bydevelopment of the emulsions exposed silver halide crystals in directcontiguous relationship with silver precipitating 3 nuclei, present inan effectively inhibiting concentration, with a processing compositioncontaining a silver halide solvent.

Photosensitive silver halide emulsions of the high speed type generallyemployed for photographic reproduction are characterized by the presenceof photoresponsive silver halide crystals possessing active senstivitycenters or sites which are believed to comprise minute aggregates ofsilver sulfide, the sulfide of which is derived from active sulfurnaturally present initially in the polymeric matrix, for example, agelatin matrix, or added to the formulation during fabrication. Foroptimum sensitivity there should be a limited but effective number ofsensitivity sites in each crystal, particularly at the surface of thecrystals. Upon exposure to incident electromagnetic radiation actinic tothe crystals, it is understood that photons absorbed by the crystalsprovide photoelectrons within the crystals which are capable ofdiffusion to the sensitivity sites which possess a lower conductivitybond level and, in effect, provide such sites with a negative chargewhich precipitates, at the sites, as elemental silver, free silver ionsoriginally disposed Within the crystal lattice. During development ofthe exposed silver halide crystals, the silver halide developing agent,a reducing agent, provides additional electrons which serve to effectprecipitation of additional silver ion of the crystals resulting in theextrusion of fiberous or filamentary elemental silver at surfacesensitivity sites and which continues until reduction of the crystals iscomplete.

The presence of the silver precipitating nuclei contiguous the silverhalide crystals during the development process effectively acts tosubstantially prevent the microscopic elemental silver filament or fiberextrusion beyond the crystal surface with the concomitant result ofrestricting image grain size to that of the crystal. Accordingly, thecovering power of the resultant negative image in each instance islimited to that provided by elemental silver grains or particlespossessing a diameter substantially equally to that of the originalcrystals dispersed in the photosensitive matrix and absent amplificationdue to the diameter increase of conventional negative image elementsresultant from filamentary image silver.

For the purpose of insuring the production of a positive imagepossessing a high covering power, the silver precipitation nuclei willbe disposed Within the photosensitive silver halide emulsion in aconcentration per unit area effective to cause image silver derived fromunexposed silver halide crystals to possess the desired opacity pergiven mass of in situ reduced silver.

Reference to the photomicrographs comprising FIGS. 2 to 6, inclusive, ofthe drawings, further illustrates in factual detail the precedingdiscussion. FIG. 2 is a photomicrograph, having a magnification factorof 128011, ofintegral positive and negative image silver in a maximumdensity area, provided in accordance with the present invention,employing a film unit fabricated and processed as detailed hereafter.For the purposes of direct comparison with the results detailed in thephotomicrograph of FIG. 2, FIG. 3 is a photomicrograph, having the samemagnification, of positive diffusion transfer image silver in acorresponding maximum density area, provided in accordance with thedisclosure of U.S. Pat. No. 2,861,885, discussed above, employing a filmunit fabricated and processed as detailed hereafter. As can be readilyobserved from examination of the respective photomicrographs, thecovering power of the image provided by the film unit fabricated andprocessed in accordance with the present invention clearly exceeds thatof the comparative film unit by a grossly extensive margin. It wouldappear that the high covering power properties of FIG. 2s film unit maybe due, in large part, to the unexpectedly efficient utilization ofsilver accorded by reason of the present invention; the specificmathematical percent gain of which is detailed hereafter.

FIG. 4 is a photomicrograph of integral negative and positive imagesilver, in a minimum density area, of the image provided by the filmunit of FIG. 2 and at the same magnification. Again, for the purpose ofdirect comparison with the results detailed in the photomicrograph ofFIG. 4, FIG. details negative image silver formation in a correspondingmaximum density area of the film unit of FIG. 3s silver halide emulsionstratum at the same magnification. Analogous to the comparativeevaluation of FIGS. 2 and 3, FIGS. 4 and 5 clearly detail theundesirably high negative covering power of the image in FIG. 5, byreason of the aforementioned amplification of the negative image, ascompared with the image provided in FIG. 4 by means of the presentinvention. Thus, FIGS. 2, 3, 4 and 5 illustrate not only the greateroptical density range to be achieved by means of the present inventionin a directly comparative situation, that is, an expanded signal tonoise ratio but, in addition, the clearly depressed base density ornoise level to be achieved by the present invention.

There is directly illustrated by examination of the photomicrograph ofFIG. 6, optical density amplifying negative filamentary image silverformation in a minimum density area of the film unit of FIG. 3s silverhalide emulsion stratum, at the same magnification as the precedingphotomicrographs, which may be positioned in contiguous overlyingrelationship with the illustrated maximum density area of FIG. 3 toprovide a composite silver transfer image.

There is thus provided by means of the present invention photosensitivesilver halide crystals or grains dispersed in an environment containingsilver precipitating nuclei or agents which in the presence of a solventdeveloper composition cause exposed grains to be reduced to opaquestructures smaller in presented area than the area of the same grainsdeveloped in an identical developer composition absent suchprecipitating nuclei. Silver image masses derived from exposed silverhalide grains developed in accordance with the present invention,accordingly, possess low optical covering power as compared with thecovering power provided by identical grains developed in the samesolvent developer absent the presence of the precipitating environment.Specifically, the present invention provides for the production of adirect positive silver image in which the mass distribution of silver issubstantially uniform macroscopically and nonuniform microscopically,and in which the transmissiveness of silver image mass is a function ofthe quantity of actinic radiation which exposed the photosensitivesilver halide. The exposed silver halide grains are reduced, in situ, ascompact masses possessing low covering power simultaneously withreduction, in situ, of unexposed silver halide grains as colloidaldispersion possessing high covering power. The direct positive silverimage thus produced in situ by means of the present invention possessextraordinary high sharpness when compared with transfer processes inwhich unexposed silver halide grains are dissolved and transferred tothe ultimate image-carrying site.

In accordance with a particularly preferred embodiment of the presentinvention, the emulsion carrying the image silver is fabricated tosubstantially prevent microscopic distortion of the image conformationby preventing microscopic migration or diffusion of image elementswithin the polymeric matrix. In general, conventional photographic imageelements may ordinarily comprise a microscopically dynamic systemwithout seriously noticeable disadvantage to the conventional employmentof the image. However, for particularly accurate color reproduction inaccordance with the principles or additive color photography,microscopic distortion of image elements is preferably obviated toinsure maximization of the accuracy of image registration with theappropriate individual optical filter elements of the additive colorscreen associated with the image-carrying element. Specifically, it hasbeen found that a photosensitive silver halide emulsion, comprisingphotosensitive silver halide crystals dispersed in a 10 polymeric binderpossessing a latice effective to substantially prevent microscopicmigration or diffusion of image silver, provides color reproductionacuity particularly desired for effective color reproduction in the manner previously described.

The desired polymeric lbinder latice property may be readily achieved byselection of a polymeric material possessing the property ofsufiiciently fixing spacially image components, or a polymeric material,otherwise desired, may be modified, for example, by crosslinking and/ orhardening, to the extent necessary to provide the desired spacialmaintenance of image components, that is, a rigidity effective tomaintain positive image components in registration with the individualoptical filter elements of the color screen through which thephotosensitive emulsion was exposed. For example, the preferredpolymeric binder material, that is, gelatin, may be hardened by contactwith conventional hardening agents to the extent necessary to providethe desired rigidification of the photographic image. Where desired,discrete particulate materials facilitating increased processingcomposition penetration of the photosensitive element, withoutdeleterious effect on the polymeric matrixs lattice, may beadvantageously incorporated in the photosensitive element for thepurpose of expediting processing of the element.

In a preferred embodiment of the present invention, the photosensitivesilver halide emulsion will be fabricated, as further specificallydetailed hereinafter, to provide a differential of 1.5 density unitsbetween the maximum image density of the developed negative silver imageand the maximum image density of the developed positive silver image. Ina particularly preferred embodiment, the photosensitive silver halideemulsion will be fabricated to provide a maximum image density of lessthan about 0.5 and, more particularly, less than about 0.3 density unitsupon development of completely exposed areas of the emulsion and willpossess silver precipitating nuclei in a concentration effective toprovide a maximum image density in excess of about 2.0 and, mostpreferably, in excess of about 2.4 density units upon development ofunexposed areas of the emulsion. In such preferred embodiment, thesilver halide emulsion will ordinarily comprise not less than 50milligrams per foot square silver halide, based on weight of silver,preferably, as a mixed silver halide and, more preferably, as silveriodobromide, particularly that containing about 1 to 9 percent iodide,by weight of silver, dispersed in a permeable colloid binder which, inthe preferred embodiment, comprises gelatin sufficiently hardened toprovide the last-mentioned optical parameters and a hydration factor,upon contact of aqueous processing composition preferably possessing apH in excess of about 12, effective to prevent swelling in excess of amagnitude equal to its ambient size within a period of less than about15 seconds.

Referring to FIG. 1, there is shown a diagrammatic enlargedcross-sectional view of a film unit constructed in accordance with apreferred embodiment of the present invention. The film unit is shown tospecifically comprises a flexible transparent film base or supportmember 10 carrying on one surface, in order, an additive color screen 11comprising a geometrically repetitive plurality of actinicradiation-filtering colored elements including a set or group of primaryred-colored filter elements, a set of primary blue-colored filterelements and a set of primary green-colored filter elements arranged ina repetitive distribution in side-by-side relationship in asubstantially single plane, and a photosensitive silver halide emulsion12 containing dispersed therethroughout silver precipitating nuclei.

The photoresponsive material of photographic emulsion 12 will, aspreviously described, preferably comprise a crystal of a compound ofsilver, for example, one or more of the silver halides, such asphotosensitive silver chloride, silver iodide, silver bromide, or mixedsilver halides, such as silver chlorobromide or silver iodobromide, ofvarying halides ratios and varying silver concentrations dispersed in aprocessing composition permeable binder material which additionallycontains silver precipitating agents dispersed throughout the emulsionin a concentration effective to provide a vigorous elemental silverprecipitating environment which causes the elemental silver depositedtherein in terms of the unexposed areas of the emulsion, as a functionof its point-to-point degree of exposure, in comparison with exposedareas of the emulsion, to possess with high covering power, that is,opacity per given mass of reduced silver.

In general, silver precipitating nuclei comprise a specific class ofadjuncts well known in the art as adapted to effect catalytic reductionof solubilized silver halide specifically including heavy metals andheavy metal compounds such as the metals of Groups IB, II-B, IVA, VIA,and VIII and the reaction products of Group IB, II-B, IVA, and VIIImetals with elements of Group VIA, and may be effectively employed in arelatively low concentration in the order of about 125 l0 moles/ft.

Especially suitable as silver precipitating agents are those disclosedin U.S. Pat. No. 2,698,237 and specifically the metallic sulfides andselenides, there detailed, these terms being understood to include theselenosulfides, the polysulfides, and the polyselenides. Preferred inthis group are the so-called heavy metal sulfides. For best results itis preferred to employ sulfides whose solubility products in an aqueousmedium at approximately 20 C. vary between 10- and 10', and especiallythe salts of zinc, copper, cadmium and lead. Also particularly suitableas precipitating agents are heavy metals such as silver, gold, platinumand palladium and in this category the noble metals illustrated arepreferred and are generally provided in the matrix as colloidalparticles.

The preferred silver halide type photographic emulsion 12, employed forthe fabrication of the photographic film unit, may be prepared byreacting a water-soluble silver halide, such as ammonium, potassium orsodium bromide, preferably together with a corresponding iodide, in anaqueous solution of a peptizing agent such as colloidal gelatinsolution; digesting the dispersion at an elevated temperature, toprovide increased crystal growth; washing the resultant dispersion toremove undesirable reaction products and residual water-soluble salts,for example, employing the preferred gelatin matrix material, bychilling the dispersion, noodling the set dispersion, and washing thenoodles with cold water, or, alternatively, employing any of the variousfloc systems, or procedures, adapted to effect removal of undesiredcomponents, for example, the procedures described in U.S. Pats. Nos.2,614,928; 2,614,929; 2,728,662, and the like; afterripening thedispersion at an elevated temperature in combination with the additionof gelatin or such other polymeric material as may be desired andvarious adjuncts, for example, chemical sensitizing agents and the like;all according to the traditional procedures of the art, as described inNeblete, C. B., Photography-Its Materials and Processes, 6th ed., 1962.

Optical sensitization and preferably panchromatic sensitization of theemulsions silver halide crystals may then be accomplished by contactwith optical sensitizing dye or dyes; all according to the traditionalprocedures of the art, or described in Hamer, F. M., The Cyanine Dyesand Related Compounds.

Subsequent to optical sensitization, any further desired additives, suchas coating aids and the like, may be incorporated in the emulsion andthe mixture coated on color screen 11 according to the conventionalphotographic emulsion coating procedures known in the art.

As the binder for the photoresponsive material, the aforementionedgelatin may be, in whole or in part, relaced with some other naturaland/ or synthetic polymeric material such as albumin; casein; or zein;or resins such as a cellulose derivative, as described in U.S. Pats.

12 Nos. 2,322,085 and 2,541,474; vinyl polymers such as described inU.S. Pats. Nos. 2,253,078; 2,276,322; 2,276,- 323; 2,281,703; 2,310,223;2,311,058; 2,311,059; 2,414,- 208; 2,461,023; 2,484,456; 2,538,257;2,579,016; 2,614,- 931; 2,624,674; 2,632,704; 2,642,420; 2,678,884;2,691,- 582; 2,725,296; 2,753,264; and the like.

Production of color screen 11, in accordance with the art, may beclassified into two major groups.

First, color screens may be prepared by totally mechanical means, as forexample, by printing or ruling a dyeable substrate, for example, with agreasy ink formulation, in accordance with the desired filter pattern;subjecting the substrate to suitable coloration, in areas which do notpossess the repellant ink mask; effecting removal of the mask; andrepeating this procedure, in accordance with the geometrical pattern offilter elements desired, a sufficient number of times to provide thedesired multiplicity of diversely colored filter elements.

A second mechanical method comprises directly printing a carriersubstrate with the desired dye formulations in accordance with thepredetermined filter pattern and repeating this printing procedure asufficient number of times to provide the multiplicity of colored filterelements desired.

A third mechanical method comprises depositing, as an irregular filterscreen pattern, a thin layer comprising a random distribution of smallgrains, such as starch grains, which have been independently coloredwith the colors desired for optical filtering effects.

The second major type of color screen production procedures comprisesphotomechanical methods of the type initially proposed by, for example,Ducos Du Hauron in the nineteenth century. These procedures comprise, ingeneral, coating a suitable support or film base with an adhesivecomposition having coated thereon a photosensitive colloid composition,as for example, dichromated gelatin; effecting exposure of the sensitivegelatin layer by incident actinic radiation, through a suitable maskwhich provides an exposure pattern devised in accordance with thedesired optical filter element arrangement; effecting differentialhardening of the sensitized material as a function of the point-to-pointdegree of exposure; removing unexposed unhardened material by solventcontact; and then subjecting the remaining hardened material to asuitable dyeing procedure in order to provide a firstcolored opticalfilter element series. This procedure is then repeated, empolyingappropriate masks, as often as necessary to provide the number ofoptical filter element types desired in the final color screen element.

Because mechanical methods of producing color screen by mechanicalprinting or ruling methods inherently require a great number ofmechanically exact printing steps to provide a finished product, andthus possess the relative high cost inevitable to such complexity ofproduction, and methods of mechanically producing mosaic type colorscreen elements have, in general, provided elements inherently lackingin color balance, due to areas posessing a predominance of particles ofone color, that is, statistical clumping, as a practical result ofattempted random distribution, and require the employment of extremelyfine colored grains in order that formation of random aggregates of thesame color may be decreased, which, however, gives rise to theadditional disadvantage that the thus-prepared units then require veryfine grain photographic emulsions and are thus "restricted to employmentin low speed photographic processes, experience as determined thatphotomechanical methods of color screen production are to be preferred,especially for high volume, low cost manufacturing operations forproduction of screen of commercially significant optical acuity.

Although color screen may be produced by traditional contact printing orprojection type photomechanical processes, a particularly preferredprocess for the production of color screen comprises the process setforth in U.S. Pat. No. 3,284,208 which includes, in essence,successively coating the smooth surface of a lenticular film with aplurality of photoresponsive layers and sequentially subjecting thecoatings to selectively displaced radiation incident on, and focused bythe lenticules receiving same, in order to provide selective exposure ofthe coating. Subsequent to each exposure, unexposed coating is removedand the resultant resist dyed in order to prolvide a series of chromaticfilter elements, prior to the deposition of the next succeedingphotoresponsive layer. Each such exposure is derived fromelectromagnetic radiation incident on the lenticular film at an angulardisplacement specifically adapted to provide the desired plurality ofchromatic filter element series in substantial side-byside or screenrelation-ship and adapted to filter predetermined wavelengths of light.

The line depth exposure of the photoresponsive layers may be accuratelycontrolled by suitably varying the in tensity or time of the incidentradiation and the color screen itself may be continuous or discontinuousand, in the former instance, may comprise an endless or seamlesselement.

For the preparation of the preferred trichromatic additive screens, theexposed area of each photoresponsive area will generally comprise aboutone-third of the layer contiguous each lenticule reeciving exposingradiation. Although all three exposures may be accomplished by radiationincident on the lenticules of the lenticular film at three separateangles each adapted to provide exposure about one-third of the areacontiguous each lenticule receiving radiation, it will be recognizedthat the terminal chromatic filter formation may also be provided byexposing the terminal photoresponsive layer to diffused radiationtraversing through the lenticular film and masked by the previouslyformed chromatic filter elements. Where desired, one or more sets ofimages resultant from exposure may be overlapped to decrease variationin the width of the exposed areas. While it is not essential that theexposing radiation incident on each lenticule form exactly the sameangle of incidence, with respect to the axis of that lenticule, as informed between radiation incident on other lenticules, and theirrespective axes, the more identical the correspondence between theangular pattern of incident radiation the greater the facility ofregistering the respective filter elements and the more uniform theresultant color screen.

At a stage subsequent to formation of the first and second series offilter elements, the lenticular configuration will be constituted as acontinuous smooth surface. In the instances where the lenticulescomprise a separate stratum temporarily aflixed to the surface of asupport on which the color screen is formed, such separate stratum maybe stripped from the support. Alternatively, where the lenticulescomprise an integral component of the film base or support and have beenprovided to the base by pressure and/or solvent deformation of the base,a continuous smooth surface may be reconstituted by application ofsuitable solvent and the deformation pressures produced during themanufacturing of lenticular film base released to provide reconstitutionof the bases original configuration. Where desired, for example, foroptical transmission purposes, the reconstituted surface may bepolished, for example, by surface contact with an appropriate rotatingpolishing cylinder or drum, for the time interval necessary to providethe desired optical characteristics to the film base surface.

Optionally the external surface of the multichromatic screen may beovercoated with a protective polymeric composition, such asnitrocellulose, cellulose acetate, and the like, for the purpose ofprotecting the screen from processing composition deformation duringemployment of the resultant film unit. The external surface of the colorscreen may then have applied thereto silver halide emulsion layer 12.

Apparatus particularly adapted to facilitate effecting exposure of thelenticular film in accordance with the afore- 14 mentioned U.S. Pat. No.3,284,208 is disclosed and claimed in U.S. Pat. No. 3,318,220.

Support or film base 10 may comprise any of the various types oftransparent ridged or flexible supports, for example, glass, polymericfilms of both the synthetic type and those derived from naturallyoccurring products, etc. Especially suitable materials, however,comprise flexible transparent synthetic polymers such as polymethacrylicacid, methyl and ethyl esters; vinyl chloride polymers; polyvinylacetals; polyamides such as nylon; polyesters such as the polymericfilms derived from ethylene glycol terephthalic acid; polymericcellulose derivatives such as cellulose acetate, triacetate, nitrate,propionate, butyrate, acetatebutyrate, or acetate propionate;polycarbonates; polystyrenes; and the like.

The present invention will be illustrated in greater detail inconjunction with the following specific example which sets forth arepresentative fabrication of the film units of the present invention,which however, is not limited to the detailed description herein setworth but is intended to be illustrative only.

The smooth surface of a lenticular film comprising a polyester film basehaving bonded to one surface a cellulose acetate butyrate layercomprising 550 lenticules per inch, each having a lano-convexconfiguration for condensing the incident radiation into converging raysand having a focal length generally in the order of about microns in airand, as a result of this short focal length, imaging objects over aboutone inch from the lens surface at infinity, may be coated on theopposite surface with an adhesive composition comprising 70 cc. ofmethanol, 1.25 grams of nitrocellulose, and 30 cc. of butyl alcohol. Afirst layer of gelatin sensitized by the addition of 15 weight percentpotassium dichromate (based on dry gelatin), may then be coated on theexternal surface of the first adhesive layer. The first gelatin layermay then be exposed to ultraviolet radiation, in accordance with thepreviously detailed explanation, and the resultant photoexposed carriersubjected to a water wash in order to provide removal of unexposedsensitized gelatin, in accordance with the exposure pattern contained inthe first gelatin layer. The web may then be treated with an acid dyeingbath comprising 1.17% Direct Red Cl. 81; 0.32% Direct Yellow Cl. 4; and2.95% glacial acetic acid, rinsed to eifect removal of excess dye, driedand a second adhesive composition containing 7 0 cc. of methanol, 30 cc.of butyl alcohol, and 1.25 grams of nitrocellulose overcoated thereon. Asecond layer of gelatin sensitized by the addition of 15 weight percentpotassium dichromate may be coated on the second adhesive layer. Thesecond photosensitized gelatin layer may be also exposed to ultravioletradiation in accordance with the previously detailed description. Thesecond gelatin layer may then be washed with water to effect removal ofunexposed photosensitive gelatin, in the manner previously detailed, andthe remaining gelatin resist dyed by contact with an acid dyeing bathcontaining 0.83 Acid Green Cl. 7; 0.32% Direct Yellow Cl. 4; and 2.86%glacial acetic acid. The web may then be rinsed to effect removal of anyresidual excess dye, dried and coated with a third adhesive compositioncomprising 30 cc. butanol, 1.25 grams of nitrocellulose, and 70 cc. ofmethanol. A third layer of gelatin sensitized with 15 weight percentpotassium dichromate may then be coated on the external surface of thethird adhesive layer and the third photosensitive gelatin layersubjected to exposure by ultraviolet radiation, in accordance with thedescription detailed previously. The third layer of photosensitivegelatin may then be washed in order to provide the desired resistformation and the resultant resist dyed by contact with a solutioncontaining 1.0% Blue T Pina and 1% glacial acetic acid, washed to effectremoval of residual dye and dried. A protective overcoat layer may beprovided by coating the external surface of the multicolor screenelement with a composition comprising 70 cc. methanol, 30 cc. butanol,and 5 grams of nitrocellulose.

Subsequent to formation of the color screen, the lenticulated celluloseacetate butyrate may be removed from the polyester base and the externalsurface of the polymeric protective coating may be coated with acomposition comprising gelatin, deacetylated chitin and 4,6-diamino-ortho cresol at a coverage of 3.75 mgs./ft. gelatin, 3.75mgs./ft. deacetylated chitin and 0.7 mgs/ ft. diamino-ortho cresol. Onthe external surface of the gelatin layer a hardened gelatino silveriodobromide emulsion containing cadmium sulfide and silica may then becoated at a coverage of 200 mgs./ft. gelatin, 100 mgs./ft. silver, 0.97mgs./ft. cadmium sulfide, 0.026 1ngs./ft. chrome alum, 0.78 mgs./ft.algiu, and 200 mgs./ ft. silica. The resultant film unit may then beadvantageously overcoated with a hardened gelatin composition at acoverage of mgs./ft. gelatin, 0.013 mgs./ft. chrome alum, 0.39 mgs./ft.algin, and 50 mgs./ft. silica.

The gelatino silver iodobromide emulsion employed may be prepared byheating a mixture comprising 80 grams of gelatin in 880 grams of waterat a temperature of about 40 C. for the period required to dissolve thegelatin. The pH of the resultant solution may be adjusted to 1010.1 and8.8 grams of phthalic anhydride in 61.6 cc. of acetone added to thesolution over a period of minutes. Subsequent to addition of thephthalic anhydride the reaction mixture may be maintained at the statedtemperature and pH for a period of about 30 minutes and then adjusted toa final pH of about 6.0.

To a solution comprising 226 grams of the gelatin phthalic anhydridederivative, prepared as above. 161 grams of potassium bromide, 2 gramsof potassium iodide, and 1200 grams of water may be added a solutioncomprising 200 grams of silver nitrate in 1600 grams of water, at a rateof about 140 cc. per minute, for a period of about 3 minutes, held 10minutes and the addition continued for a period of about 9 minutes. Theresulting emulsion may then be precipitated by reducing the pH to about2.5-3.0 with sulfuric acid. The precipitate may then be separated fromthe supernatant liquid and washed until the wash water is essentiallyfree of excess potassium bromide. Ninety-five grams of gelatin may thenbe added to the precipitate, the volume adjusted with water to 845 cc.,and dissolved by heating to about 38 C., for about 20 minutes, at a pHof about 56, and about 1.0 cc. of 1 N potassium bromide added to theemulsion. To the reaction mixture, at about 56 C., may be added about 5cc. of a solution containing 0.1 gram of ammonium thiocyanate in 9.9 cc.of water and 0.4 cc. of a solution containing 0.097 gram of goldchloride in 9.9 cc. of water, and the mixture ripened at thattemperature for about 37 hours. The resultant emulsion may then bepanchromatically sensitized by the sequential addition of 0.1%, :byweight, methanol solutions of anhydro 5,5'-diphenyl- 3,3bis-(4-sulfobutyl)-9-ethyl-oxacarbocyanine hydroxide and anhydro5,5-dimethyl-3,3'-bis-(3-sulfopropyl)-9-ethylthiacarbocyanine hydroxidein optionally effective concentrations. To the resultantpanchromatically sensitized silver iodobromide emulsion, there may thenbe provided, prior to coating, the cadmium sulfide silver precipitatingagent, formed in situ by the addition of substantially equimolarquantities of cadmium nitrate and sodium sulfide solutions, and thesiliceous porosity providing an antiswelling agent.

The film unit, fabricated as detailed above, may be subjected toexposing electromagnetic radiation incident on the transparent base anddeveloped by contacting the film unit for about 2 seconds with aprocessing composition comprising 180 cc. of water, 8.33 grams of sodiumhydroxide, 16 grams of sodium thiosulfate, 6.48 grams of sodium sulfite,0.42 gram of 6-nitrobenzimidazole, and 5 grams of2,6-dimethylhydroquinone, to provide production of a positive silverimage possessing the optical characteristics described hereinbefore andthe acuity required for additive color reproduction.

A film unit fabricated and processed in the manner detailed aboveexhibited a D silver coverage of mgs./ft. and a D silver coverage of 166mgs./ft. and an optical density of 2.90 and 0.65, respectively. Thecovering power of the film equaled at Dmax, 179 and at D 37.5 calculatedas Optical Density Comparison of a film unit fabricated and processed inthe manner detailed above, versus a film unit fabricated and processedin the same manner with the exception that the stated silverprecipitating nuclei were dispersed in a separate processing compositionpermeable layer coated on the surface of the photosensitive silverhalide emulsion opposite that carrying the color screen and from whichfilm unit the photomicrographs denoted as FIGS. 3, 5 and 6 wereprovided, clearly illustrates the highly efficient utilization of silverprovided by means of th present invention. Specifically, a film unitfabricated and processed in accordance with the present invention,possessing an initial silver coverage of 128 mgs./ft. prior to exposureand processing, provided subsequent to exposure and processing in imageD areas 118 mgs./ft. of positive and negative image silver for a percentsilver utilization in the order of 92%. In contradistinction, acomparative film unit possessing the silver precipitating nucleidisposed in a separate layer contiguous the photosensitive silver halideemulsion layer, possessing an initial silver coverage of 133 mgs./ft.prior to exposure and processing, exhibited subsequent to exposure andprocessing in areas of maximum positive image density 61 mgs./ft. ofpositive image silver and an overlying negative image silver coverage of40 mgs./ft. for a total percent silver utilization of 76 percent.

Additional film units may be fabricated and processed in the mannerdetailed above and optimized to exhibit a D of 3.3 and a D of 0.3 and tothus provide a differential of 3.0 density units and, in effect, apercent transmission ratio of about 1,00021, and, where desired, forexample, by reason of selected color screen parameters, a D,,,,,,; of4.0 and a D of 0.3 to provide a differential of 3.7 density units andthus a percent transmission ratio of about 5,000zl.

In contradistinction to developed negative image silver in conventionalprocesses, including the silver diffusion transfer reversal processidentified above as providing the photomicrographs of FIGS. 3, 5 and 6,film units fabricated and processed in accordance with the presentinvention clearly exhibit substantially no negative image fiber orfilament formation and, accordingly, substantially no negative imageamplification resultant from such conformation.

The film units of the present invention are particularly desirable foremployment as a cin film for additive colormotion picture projection, inaddition to slide tranparency film, by reason of the inherent ability tosimply and effectively process such film employing relatively simple andstable processing compositions, immediately subsequent to exposure,without the necessity of providing a process and apparatus adapted toeffect stripping of a separate emulsion stratum from the remainder ofthe film unit, to provide color information recordation possessing theimage integrity and reproduction characteristics required for effectiveemployment of the film.

As denoted by the illustrative example, the photosensitive silver halideemulsion may have advantageously incorporated therein discreteparticulate materials providing increased porosity to the emulsion,without deleterious effect on the dimensional stability of the emulsionbinder lattice, in particular, those materials which additionally act asan antiswelling agent for the emulsions polymeric binder material and,accordingly, act to facilitate the prevention of the polymer carriedimages microscopic distortion, particularly, with respect to anassociated color screen, such as discrete silica particles dis 17persed, for example, in a concentration of about 0.3 to 1.5 parts silicaper part polymer, for the purpose of facilitating processing compositionpermeation of the emulsion. In addition, the emulsion stratum may beadvantageously overcoated with a processing composition permeablepolymeric material such as a hardened gelatin pad or the like toadvantageously promote uniformity in processing composition premeationof the emulsion, by

modulating any Wave front resultant from initial surface contact withthe liquid employed and to thereby promote uniform maintenance of thepolymeric binders physical characteristics.

Although the illustrative example employed chrome alum and particularlyalgin as hardening agents for the polymeric gelatin emulsion binder anda hardening agents for the polymeric gelatin overcoat, it will berecognized that substantially any hardening or crosslinking agent may beemployed, where necessary, which does not provide deleteriousphotographic effects, to the extent required to provide a polymericlattice which effectively inhibits to a substantial effect, migration ofimage silver. An extensive collection of hardening agents are disclosedin the art as specifically adapted to effect hardening or crosslinkingof photographic polymeric binder material compositions and by reason oftheir innocuous photographic effects are to be preferred in the practiceof the present invention. The sole requirement for effective operationof the film unit is that the emulsions polymeric lattice be constructedto provide the optical image parameters denoted hereinbefore. Thus,substantially any conventional hardening and crosslinking agent may beselected from those set forth throughout, for example, the pertinentpatent literature regarding such agents, and the concentration employed,as known in the art, will be dependent upon the relative activity of theselected agent, or agents, and the relative amount of hardening orcrosslinking to be effected. The specific concentration of a selectivehardening or crosslinking agent, to be contacted with a selectedpolymeric binder, may be readily determined empirically, within thespecific context of ultimate photographic employment, by screening. Itwill be further recognized that any of the various processingcomposition permeable, synthetic or natural polymeric materials,possessing the physcial characteristics required to provide the resultsdenoted above, may be substituted in replacement of the specificallyillustrated polymeric material, gelatin, provided that such selectedpolymer provides a matrix which is not deleterious to photosensitivesilver halide crystals and possesses a lattice allow ing development inthe manner previoiusly described.

Suitable silver halide solvents for employment in the practice of thepresent invention include conventional fixing agents such as thepreviously noted sodium thiosulfate, sodium thiocyanate, ammoniumthiocyanate, the additional agents described in U.S. Pat. No. 2,543,181,and the associations of cyclic imides and nitrogenous bases such asassociations of barbiturates or uracils and ammonia or amines and otherassociations described in UJS. Pat. No. 2,857,274.

Where desired conventional silver toning agent or agents may be disposedwithin the emulsion composition in a concentration effective to providea positive image toned in accordance with the desires of the operator.

In the preferred embodiment of the present invention, the processingcomposition will include an alkaline material, for example, sodiumhydroxide, potassium hydroxide or sodium carbonate, or the like, andmost preferably in a concentration providing a pH to the processingcomposition in excess of about 12. The processing composition may, wheredesired, contain the sole silver halide developing agent or agentsemployed, or a silver halide developing agent in addition to thatdisposed within the film unit; however, disposition of one or moredeveloping agents in the emulsion and/or a permeable layer directlyassociated therewith, intermediate the emulsion and a color screen, is aparticularly preferred embodiment, for the purpose of providingunexposed image acuity, which more readily facilitates directlyinitiated development at radiation exposed areas of the emulsion withoutthe necessity of diffusing such agents to such sites by means of theprocessing composition selected.

It will be apparent that the relative proportions of the agentscomprising the developing composition set forth herein may be altered tosuit the requirements of the operator. Thus, it is within the scope ofthis invention to modify the herein described developing compositions bythe situation of preservatives, alkalis, silver halide solvents, etc.,other than those specifically mentioned. When desirable, it is alsocontemplated to include, in the developing composition, components suchas restrainers, accelerators, etc. The concentration of such agents maybe varied over a relatively wide range commensurate with the art.

The processing composition solvent employed, however, will generallycomprise water and will possess a solvent capacity which does notdeleteriously hydrate the selected emulsion polymers lattice beyond thatrequired to provide the preferred image formation. Accordingly, noadjunct should be included within such composition which deleteriouslyeffects the lattice parameters required for such image formation.

In the description herein, each color series of filter elements has beendescribed as covering that part of the total area in proportion to thetotal number of colors used, i.e., in the tricolor system, each coloroccupies one-third of the total area. This may vary quite widely beforehaving a noticeable effect to the observer and, in fact, may becompensated by changing the intensity of the colors. In actual practice,if one dye is of greater intensity than the others, a deliberatecompensation may be made by reducing the total relative area of theintense color. The aspect of relative areas is well known in the art sothat when relative areas are used in this application, it is intended toinclude the variances which the art would recognize as being successful.

Various colors and numbers of colors may be used in this invention butthe preferred system, as previously mentioned, is a tricolor arrangementof the three primary colors, red, green and blue.

It will be recognized, however, that, in accordance with the instantdisclosure, a plurality of chromatic filter element series may beprovided, the number of series being solely determined by the opticalparameters of the resultant color screen desired.

For example, a four-color system such as red, green, violet-blue andorange-yellow could also be effectively employed in accordance with theteachings of the instant disclosure.

In the practice of the present invention, additive trichromatic colorscreens possessing 550, 756 and 1100 lines/color/inch have been employedand it has been found that image resolution obtained by means of thepresent invention exceeds that obtainable in processes which requiretransfer of image-forming components to, or from, the ultimate imagecarrying layer contiguous the color screen. Such increased resolutionspecifically facilitates the acuity of color reproduction to be achievedby the practice of the invention.

In general, the silver halide emulsion will preferably contain theminimal grain size distribution commensurate with the process speeddesired for selected employment of film unit fabricated in order tomaximize the average number of grains located behind any one opticalfilter element and to further maximize the resolution achieved by thefilm units construction. The emulsion will also preferably bepanchromatically sensitized to provide equal image production, as adirect function of incident exposing radiation, throughout the responseportion of the radiation spectrum to further enhance the acuity of colorinformation recordation by the emulsion.

In addition to the described essential layers, it will be recognizedthat the film unit may also contain one or more subcoats or layers,which, in turn, may contain one or more additives such as plasticizers,intermediate essential layers for the purpose, for example, of enhancingadhesion, and that one or more of the described layers may comprise acomposite of two or more strata which may be contiguous or separatedfrom each other.

Since certain changes may be made in the above product, process andapparatus without departing from the scope of the invention hereininvolved, it is intended that all matter contained in the abovedescription shall be interpreted as illustrative and not in a limitingsense.

What is claimed is:

1. A photographic film unit which comprises a multicolor screen carryingon one surface a photosensitive silver halide emulsion comprisingphotosensitive silver halide crystals which contain at least two halidesselected from the group consisting of iodide, bromide and chloride andsilver precipitating nuclei.

2. A photographic film unit as defined in claim 1 wherein said silverprecipitating nuclei are present in a concentration effective to providea silver image possessing optical density inversely proportional toexposure of the emulsion.

3. A photographic film unit as defined in claim 2 wherein said silverprecipitating nuclei are present in a concentration effective to providea silver image derived from unexposed silver halide crystals possessinggreater covering power than a silver image derived from exposed silverhalide crystals.

4. A photographic film unit as defined in claim 3 wherein said silverimage derived from unexposed silver halide crystals comprises silver ofa first physical character and said silver image derived from exposedsilver halide crystals comprises silver of a second physical character,said first physical character silver possessing higher optical densitythan said second physical character silver per unit mass.

5. A photographic film unit as defined in claim 4 which comprises atransparent support carrying on one surface, in order, a multicolorscreen and a photosensitive silver halide emulsion comprising, dispersedin a processing composition permeable polymeric binder, photosensitivesilver halide crystals which contain at least two halides selected fromthe group consisting of iodide, bromide and chloride and silverprecipitating nuclei present in a concentration effective to provideupon development in the presence of a silver halide solvent, as afunction of exposure, a silver image comprising said first and saidsecond physical character silver.

6. A photographic film unit as defined in claim 3 which comprises atransparent support carrying on one surface, in order, a multicolorscreen and a photosensitive silver halide emulsion comprisingphotosensitive silver halide crystals which contain at least two halidesselected from the group consisting of iodide, bromide and chlo ride andsilver precipitating nuclei in a concentration effective to provide upondevelopment in the presence of silver halide solvent, as a function ofexposure, a silver image derived from development of exposed silverhalide crystals possessing a maximum image density at least 1.5 densityunits less than the maximum density of a silver image derived fromdevelopment of unexposed silver halide crystals.

7. A photographic film unit as defined in claim 6 which comprises atransparent support carrying on one surface, in order, a multicolorscreen and a photosensitive silver halide emulsion comprisingphotosensitive silver halide crystals which contain at least two halidesselected from the group consisting of iodide, bromide and chloride andsilver precapitating nuclei dispersed in a processing compositionpermeable polymeric binder effective to substantially preventmicroscopic distortion of image components in registration withindividual multicolor screen optical filter elements through which thephotosensitive emulsion was exposed, said silver precipitating nucleipresent in a concentration effective to provide upon development in thepresence of a silver halide solvent, as a function of exposure of theunit to actinic radiation, a minimum image density not in excess ofabout 0.5 and a maximum image density of not less than about 2.0.

8. A photographic film unit as defined in claim 1 wherein said silverhalide crystals comprise silver iodobromide crystals.

9. A photographic film unit as defined in claim 8 wherein said silveriodobromide crystals comprise about 1 to 9 percent, by weight, iodide.

10. A photographic film unit as defined in claim 1 wherein saidphotosensitive silver halide crystals are panchromatically sensitized.

11. A photographic film unit as defined in claim 10 wherein saidmulticolor screen is a tricolor additive screen.

12. A photographic film unit as defined in claim 11 wherein saidadditive tricolor screen comprises red, green and blue colored opticalfilter elements.

13. A photographic film unit as defined in claim 5 wherein saidpermeable polymeric binder comprises gelatin.

14. A photographic film unit as defined in claim 13 wherein said gelatinis hardened to the extent necessary to prevent substantial microscopicdiffusion of silver image components.

15. A photographic film unit as defined in claim 14 wherein saidhardened gelatin binder contains dispersed therein silica.

16. A photographic film unit as defined in claim 15 wherein said silicais present in a concentration of about 0.2 to 1.5 parts silica per partgelatin.

17. A photographic film unit as defined in claim 1 including a separateprocessing composition permeable polymeric layer containing a silverhalide developing agent positioned intermediate said multicolor screenand said photosensitive silver halide emulsion.

18. A photographic film unit as defined in claim 1 wherein saidmulticolor screen comprises an additive multicolor screen.

19. A photographic film unit as defined in claim 1 wherein said silverprecipitating nuclei are dispersed in said emulsion in a concentrationof about 125 10 moles/ftfi.

20. A photographic film unit as defined in claim 1 wherein said silverprecipitating nuclei comprises metallic sulfides, metallic selenides orcolloidal noble metals.

21. A photographic film unit as defined in claim 20 which comprises atransparent support carrying on one surface, in order, a trichromaticadditive color screen comprising red, green and blue color opticalfilter elements and a photosensitive silver halide emulsion comprisingpanchromatically sensitized silver iodobromide crystals and metallicsulfide, metallic selenide or colloidal noble metal silver precipitatingnuclei dispersed in a gelatin binder in a concentration elfective toprovide upon development of exposed silver iodobromide crystals in thepresence of a silver halide solvent, as a function of the point-to-pointdegree of exposure to actinic radiation, a maximum silver image densitynot in excess of about 0.3 and a maximum silver image density ofdeveloped silver derived from unexposed silver halide crystals of notless than about 2.4.

22. A photographic process which comprises, incombination, the steps ofexposing a photographic film unit containing a multicolor screen and aphotosensitive silver halide emulsion comprising photosensitive silverhalide crystals which contain at least two halides selected from thegroup consisting of iodide, bromide and chloride and silverprecipitating nuclei, through said multicolor screen and contacting saidexposed emulsion with an aqueous processing composition containing asilver halide developing agent and a silver halide solvent therebyproviding a visible silver image to said emulsion in terms of theunexosed areas of said emulsion as the function of the point-to-pointdegree of emulsion exposure.

23. A photographic process as defined in claim 22 which comprises, incombination, the steps of exposing a photographic film unit containing atransparent support carrying on one surface, in order, a multicolorscreen and a photosensitive silver halide emulsion comprisingphotosensitive silver halide crystals which contain at least two halidesselected from the group consisting of iodide, bromide and chloride andsilver precipitating nuclei dis persed in a processing compositionpermeable polymeric binder in a concentration effective to provide asilver image possessing optical density inversely proportional toexposure of the emulsion, said exposure resultant from actinic radiationincident on said transparent support, and contacting said silver halideemulsion with an aqueous processing composition containing a silverhalide developing agent and a silver halide solvent to provide a visiblesilver image to said emulsion possessing optical density inverselyproportional to exposure of the emulsion.

24. A photographic process as defined in claim 23 which comprises, incombination, the steps of exposing a photographic film unit containing atransparent support carrying on one surface, in order, a multicolorscreen and a photosensitive silver halide emulsion comprisingphotosensitive silver halide crystals which contain at least two halidesselected from the group consisting of iodide, bromide and chloride andsilver precipitating nuclei dispersed in a processing compositionpermeable Polymeric binder in a concentration effective to provide asilver image derived from unexposed silver halide crystals possessinggreater covering power than a silver image derived from exposed silverhalide crystals, said exposure resultant from actinic radiation incidenton said transparent support, and contacting said silver halide emulsionwith an aqueous processing composition containing a silver halidedeveloping agent and a silver halide solvent for a period of timeeffective to provide a visible silver image to said emulsion, as afunction of emulsion exposure, derived from unexposed silver halidecrystals possessing greater covering power than the silver image derivedfrom exposed silver halide crystals.

25. A photographic process as defined in claim 24 wherein said silverimage derived from unexposed silver halide crystals comprises silver ofa first phyhical character and said silver image derived from exposedsilver halide crystals comprises silver of a second physical character,said, first physical character silver possessing higher optical densitythan said second physical character silver per unit means.

26. A photographic process as defined in claim 24 which comprises, incombination, the steps of exposing a photographic film unit containing atransparent support carrying on one surface, in order, a multicolorscreen and a photosensitive silver halide emulsion comprisingphotosensitive silver halide crystals which contain at least two halidesselected from the group consisting of iodide, bromide and chloride andsilver precipitating nuclei dispersed in a processing compositionpermeable polymeric binder in a concentration effective to provide upondevelopment, as a function of exposure, a silver image derived fromdevelopment of unexposed silver halide crystals possessing a maximumimage density at least 1.5 density units greater than the maximumdensity of the silver image derived from development of exposed silverhalide crystals, said exposure resultant from actinic radiation incidenton said transparent support, and contacting said silver halide emulsionwith an aqueous processing composition containing a silver halidedeveloping agent and a silver halide solvent for a period of timeeffective to provide a visible silver image to said emulsion in terms ofthe unexposed areas of said emulsion as a function of the point-to-pointdegree of emulsion exposure, said visible silver image derived fromdevelopment of unexposed silver halide crystals and possessing a maximumimage density at least 1.5 density units greater the maximum density ofdeveloped silver derived from development of exposed silver halidecrystals.

27. A photographic process as defined in claim 26 which comprises, incombination, the steps of exposing a photographic film unit whichcomprises a transparent support carrying on one surface, in order, amulticolor screen and a photosensitive silver halide emulsion comprisingphotosensitive silver halide crystals which contain at least two halidesselected from the group consisting of iodide, bromide and chloride andsilver precipitating nuclei dispersed in a processing compositionpermeable polymeric binder in a concentration effective to provide upondevel opment of exposed silver halide crystals a maximum silver imagedensity not in excess of about 0.5 and a maximum silver image densityderived from unexposed silver halide crystals upon development of notless than about 2.0, said exposure accomplished by actinic radiationincident on said transparent support, and contacting said silver halideemulsion with an aqueous processing composition containing a silverhalide developing agent and a silver halide solvent for a suflicienttime to provide a silver image to said emulsion comprising a maximumdensity of image silver derived from development of unexposed silverhalide crystals of not less than about 2.0 and a maximum density ofimage silver derived from development of exposed silver halide crystalsnot in excess of about 0.5.

28. A photographic process as defined in claim 23 wherein saidprocessing composition permeable polymeric binder comprises gelatin.

29. A photographic process as defined in claim 28 which comprises, incombination, the steps of exposing a photographic film unit containing atransparent support carrying on one surface, in order, a trichromaticadditive color screen and a photosensitive silver halide emulsioncomprising panchromatically sensitized silver iodobromide crystals andsilver precipitating nuclei dispersed in a processing compositionpermeable gelatin binder possessing a lattice effective to substantiallyprevent microscopic diffusion of silver image components, said silverprecipitating nuclei present in a concentration effective to provide,upon development in the presence of a silver halide solvent and as afunction of exposure, image silver derived from development of exposedsilver iodobromide crystals possessing a maximum silver image densityless than about 0.3 and maximum silver image density derived fromdevelopment of unexposed silver iodobromide crystals greater than about2.4, said exposure accomplished by actinic radiation incident on saidtransparent support, and contacting said exposed emulsion with anaqueous processing composition containing a silver halide developingagent and a silver halide solvent for a time sufficient to provide asilver image to said emulsion in terms of the unexposed areas of saidemulsion possessing a maximum silver image density of not less thanabout 2.4 and a silver image to said emulsion in terms of the exposedareas of said emulsion possessing a maximum silver image density not inexcess of about 0.3.

30. A photographic process as defined in claim 29 wherein said silverprecipitating nuclei comprises metallic sulfides, metallic selenides orcolloidal noble metals.

31. A photographic process as defined in claim 30 wherein said silverprecipitating nuclei are dispersed in said silver iodobromide emulsionin a centration of about 1 to 25 X 10- moles/ft.

32. A photographic process as defined in claim 28 wherein saidpanchromatically sensitized emulsion additionally contains silicadispersed therein.

33. A photographic process as defined in claim 22 wherein said silverhalide developing agent is disposed in 23 said film unit prior to saidcontact of said unit with said aqueous processing composition.

34. A photographic process as defined in claim 22 wherein saidmulticolor screen comprises an additive multicolor screen.

35. A photographic process as defined in claim 34 wherein saidmulticolor screen comprises a trichromatic additive color screencomprising red, green and blue chromatic filter elements.

36. A photographic process as defined in claim 22 wherein said silverhalide emulsion comprises a silver iodobromide emulsion.

37. A photographic process as defined in claim 36 wherein said silveriodobromide emulsion is panchromatically sensitized.

38. A photographic process as defined in claim 37 wherein said silveriodobromide emulsion comprises silver iodobromide crystals containingabout 1 to 9 percent, by weight, iodide.

39. A photographic product which comprises a composite film unitincluding a multicolor screen having associated therewith a developed,photoexposed silver halide stratum which comprised photosensitive silverhalide crystals including at least two halides selected from the groupconsisting of iodide, bromide and chloride containing a substantiallyuniform concentration of silver therethrough and a silver imagepossessing optical density inversely proportional to photoexposure ofsaid stratum.

40. A photographic product as defined in claim 39 wherein said silverimage includes a positive silver image in terms of unexposed areas ofsaid stratum comprising silver of a first physical character and anegative silver image in terms of exposed areas of said stratumcomprising silver of a second physical character, said first physical 24character silver possessing higher optical density per unit than saidsecond physical character silver.

41. A photographic product as defined in claim 40 wherein said positivesilver image possesses maximum density in unexposed areas of said silverhalide stratum at least 1.5 density units greater than the maximumdensity of said negative silver image in exposed areas of said silverhalide stratum.

42. A photographic product as defined in calim 41 wherein said negativesilver image possesses a maximum density in exposed areas of said silverhalide stratum not in excess of about 0.5 and a maximum denstiy of saidpositive silver image in unexposed areas of said silver halide stratumnot less than about 2.0.

43. A photographic product as defined in claim 39 wherein saidmulticolor screen is an additive multicolor screen.

44. A photographic product as defined in claim 43 wherein said additivemulticolor screen is carried on a flexible transparent support andcomprises a trichromatic color screen comprising red, green and bluecolored optical filter elements.

References Cited UNITED STATES PATENTS 2,614,926 10/1952 Land 96292,712,995 7/1955 Weyde 963 3,284,208 11/1966 Land 96118 NORMAN G.TORCHIN, Primary Examiner A. T. SURO PICO, Assistant Examiner US. 01.X.R. 96-- 118

